The overall objectives are to develop a small marsupial, Monodelphis domestica, as an economical laboratory animal for biomedical research and to make the animal and techniques for its experimental manipulation readily accessible to other investigators. The specific aims are to develop an optimal diet for the species, to simplify husbandry procedures, to identify genetic markers for research and management purposes, to progress in developing inbred strains, and to provide animals, on site research facilities, and technical expertise to other investigators. Age-matched animals will be placed in four dietary groups and assessed for growth rates, reproductive performance, and general health characteristics over two generations. In an attempt to simplify husbandry procedures, we will study matched pairs of animals in the presence or absence of next boxes in order to determine if nest boxes are effective in reducing aggressive behavior and enhancing reproductive performance. Genetic markers will be identified and characterized by electrophoretic methods. Whereas some animals will be maintained as a non-inbred stock in which genetic variability is maximally preserved, others will be used for developing inbred strains by full-sib matings. Animals, biological materials from them, and information regarding their management and experimental manipulation will be provided to other investigators upon request and by publication, and local and visiting scientists will be encouraged to use our resource for on site collaborative research. The popularity of M. domestica as an animal model for research in developmental biology, physiology, gene regulation, and other health-related fields, is continuing to increase rapidly. Our resource is by far the largest marsupial colony in the world. It is unique also in being the only marsupial colony committed to the development of husbandry and experimental procedures for this species, to genetic management of the species in captivity, to assisting visiting scientists who would not otherwise be able to pursue their research interests efficiently, and to providing animals and biological material from them to investigators at other institutions. We expect that our efforts will continue to play a critical role in the burgeoning use of M. domestica as an animal model in biomedical research.